1. Field of the Invention
This invention relates to a cooling system for electronic circuit components, such as integrated circuit chips (IC) or semiconductor elements, mounted on a printed circuit board, and more particularly, to such a cooling system including a cooling plate in which liquid coolant is circulated.
2. Description of the Related Art
A cooling plate assembly used for cooling circuit components mounted on a printed circuit board or boards is disclosed in U.S. Pat. No. 4155402. In this liquid-cooling plate assembly, a liquid-cooled, cold plate with a complaint mat interface made of a heat conductive, electrically insulating complaint structure is arranged in compression contact with diverse circuit components on a printed circuit board so that intimate contact can be achieved with the circuit components, in spite of differences in the relative heights and shapes of the circuit components.
One of the typically known examples of the above-mentioned type of cooling system is shown in FIG. 8, which is an exploded perspective view illustrating a cooling plate arranged adjacent to a printed circuit board 1 on which a plurality of electronic components 2 are mounted, so that predetermined cooling points thereof are in contact with the top surfaces of the electronic components 2. Liquid coolant, such as a cooling water, is supplied into the cooling plate 3 via an inlet, as shown by an arrow A, and discharged via an outlet, as shown by an arrow B, so that the coolant is circulated through coolant passages in the cooling plate 3 to effect a cooling operation.
FIG. 9 is a plan view illustrating an arrangement of the coolant passage in a conventionally known cooling plate; and FIG. 10 is a cross-sectional view taken along a line X--X in FIG. 9. A cooling plate 10 in this example includes lower and upper horizontal main passages 11a and 11b and a plurality of vertical branch passages 12 connected therebetween. These main passages 11a and 11b are closed at their opposite ends by means of closing plugs 13a and 13b, respectively, in case the cooling plate 10 is manufactured by a process of machining.
Therefore, the coolant supplied, as shown by an arrow A, through one of the main passage 11a is separated and flows into the respective branch passages 12, as shown by the arrows A1. Then, the coolant confluences, as shown by arrows B1, and is discharged from the cooling plate 3, as shown by an arrow B.
FIG. 11 is a plan view illustrating an arrangement of the coolant passage in another example of a conventionally known cooling plate. In this case, a cooling plate 20 includes a single zig-zag passage 21. The coolant supplied as shown by an arrow A flows through the zig-zag passage 21 and is discharged from the cooling plate 20 as shown by an arrow B.
FIG. 12 is a cross-sectional view illustrating heat exchange elements 14 which can be provided in the cooling plate 10 or 20 as mentioned above with reference to FIGS. 9, 10 and 11. The heat exchanger element 14 made of a resilient or flexible member, such as a bellows, is rigidly attached to the cooling plate 10 or 20 on a coolant chamber 17 provided on a way of the branch passage 12 of the cooling plate 10 or the zig-zag passage 21 of the cooling plate 20.
The cooling plate 10 or 20 is vertically arranged adjacent to and in parallel with a printed circuit board 1 and maintained at a predetermined gap by means of spacer blocks 15 inserted therebetween, so that the top surfaces of the heat exchanger elements 14 are in resilient contact with the electronic components 2 mounted on the printed circuit board 1.
Therefore, the liquid coolant supplied into the branch passages 11 or the water passage 21, as shown by the arrows Cl, is injected through nozzles 16 toward the elements 14 as indicated by the arrows C2. After the injection, the coolant flows into the next section of the branch passage 11 or the zig-zag passage 21, as shown by the arrows C3, and the same operation is repeated. Finally, the coolant flows out of the last cooling chamber 17 into the branch passage 11 or the passage 21.
However, according to the conventional cooling plate as mentioned above, when draining the coolant from the cooling plate is necessary, such as when the relevant electronic system is stopped for maintenance or transferred to another place, a part of coolant remains in blind portions, as indicated by reference E, of the coolant chambers 17 in the example shown in FIG. 9, or the bottom U-shaped blind portions, as indicated by reference F, of the zig-zag passage 21 in the example as shown in FIG. 11, even if the liquid coolant was drained from the respective inlet or outlet ports, by charging high-pressure gas from the opposite entrance. Therefore, the liquid coolant cannot be completely discharged from the conventional cooling plate 10 or 20. Also, if a part of coolant remains in the cooling plate, a damage to the electronic circuit components might occur due to an expansion of coolant and the cooling system might be sufferred from corrosion when the coolant freezes.
And more, when the pressure of the coolant changes rapidly or vibrates, such as water-hammer or ripple, the pressure in the cooling chamber 17 as shown in FIG. 12 becomes unstable and dangerous for electric circuit components.